Forests are another piece of the global warming puzzle

March 13, 2009

Forests — along with grasslands, soils, and other ecosystems — are an important part of the equation (Credit: Denis Giles via Flickr).

By David Suzuki with Faisal Moola

We know that global warming is a reality and that we humans are its primary cause. And we know that carbon dioxide emissions, in large part from burning fossil fuels, are one of the biggest contributors to global warming. But we still have much to learn about the Earth's mechanisms when it comes to regulating emissions and warming.

Forests — along with grasslands, soils, and other ecosystems — are an important part of the equation, and a new report published in the journal Nature sheds a bit more light on their role. We've known for a long time that forests are important carbon sinks. That is, they absorb carbon from the atmosphere thus preventing it from contributing to global warming.

But the Nature study shows that tropical forests absorb more carbon than we realized. Researchers from a number of institutions, including the University of Toronto, analyzed data from 79 intact forests in Africa from 1968 to 2007, along with similar data from 156 intact forests from 20 non-African countries. They concluded that tropical forests absorb about 4.8 billion tonnes of carbon a year, equivalent to about 18 per cent of the carbon dioxide added to the atmosphere each year by burning fossil fuels. The world's oceans are the other major carbon sink, absorbing about half the human-produced carbon that doesn't end up in the atmosphere.

That doesn't mean we can count on the forests or the oceans to save us from our folly. To start, about 15 billion of the 32 billion tonnes of carbon dioxide that humans produce is not reabsorbed on land or sea and ends up in the atmosphere. And the carbon stored in forests can be released back into the atmosphere with natural disturbances, such as fire or insect outbreaks, or if the forest is logged. This is because when trees are cut down, die, and decay naturally, or burn, some of the stored carbon is released back into the atmosphere. Even if carbon remains stored in the form of wood products taken from a logged forest, some is still released when soils in the forest floor are disturbed by logging. And many wood and pulp and paper products are discarded and destroyed in a much shorter time period than the life of an old-growth forest. This means that the carbon is released earlier than it would have been if the forests were left intact.

We humans have upset the balance of nature in more ways than we understand. The scientists haven't figured out why the tropical trees are growing big enough to absorb more carbon than they release. One theory is that global warming and the extra carbon in the atmosphere are actually fertilizing the trees.

One thing we do know is that we cannot rely on tropical forests to prevent dangerous levels of climate change. But the amount of carbon they store gives us another compelling argument for protecting forests, as they may at least provide a buffer while we work on other solutions, such as reducing our energy consumption and switching to renewable sources of energy.

Clearly, it's not the only reason to protect forests. Looking at the ability of forests to absorb carbon allows us to see that they have economic value beyond resources such as lumber that we have traditionally considered. Forests are a source of medicine, food, and clean drinking water and are habitat for over half of all land-based plants and animals on the planet. Forests also provide spiritual, aesthetic, and recreational opportunities for millions of people.

Forest degradation is also contributing to another ecological crisis, a biodiversity crisis on par with earlier mass extinctions. Scientists estimate that 16,000 species are now threatened with extinction, including 12 per cent of birds, 23 per cent of mammals, and 32 per cent of amphibians. Habitat destruction is partly responsible for this crisis, and climate change is exacerbating it. And although most of our carbon emissions are from burning fossil fuels, one quarter is from deforestation.

What all this shows is how everything in nature is interconnected and how our planet works to find equilibrium. We can't confront the problems we have created on a piecemeal basis. We must look at them together. Conserving the world's forests — which can include sustainable forestry practices — is one obvious place to start dealing with some of the most imminent crises.